Path: utzoo!mnetor!uunet!husc6!think!ames!ptsfa!well!ewhac
From: ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab)
Newsgroups: comp.graphics
Subject: Re: Interactive Stereo Viewing
Message-ID: <5039@well.UUCP>
Date: 20 Jan 88 09:01:42 GMT
References: <4615@tut.cis.ohio-state.edu> <146@rocky8.rockefeller.edu> <1396@pixar.UUCP>
Reply-To: ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab)
Organization: The CIA:  Third-World Governments Destabilized While-U-Wait.
Lines: 76
Summary: You're going about it all wrong...

In article <1396@pixar.UUCP> flip@pixar.UUCP (Flip Philips) writes:
>In article <4615@tut.cis.ohio-state.edu> WAMBOLD@OSU-20 (Sandra Wambold) writes:
>>Does anyone on this BB know the proper translations and rotations for
>>interactive stereo viewing?  [ ... ]
>>
>Transform the Left & Right views by these:
>
>	[ Matricies deleted ]
>
	He goes on to explain about focal length and distance between eyes.
While I'm sure this will work, it's not nearly as intuitive (to me) as the
approach I've been using.

	You have two eyes.  These can be thought of as two cameras into a
world space, seperated horizontally by a fixed distance (2.5" typically).
Both eyes... er, cameras are looking at the same point.  So all you need to
do is calculate and render two images, one for the left camera and one for
the right.

	As said before, both camera focus on the exact same point.  If they
don't, the stereo effect will be diminished greatly.  The viewpoint (where
the line of sight of the two cameras converge) will appear precisely on the
surface of your screen.  All points between the viewpoint and the camera
will appear to leap off the screen, and all those behind the viewpoint will
sink back into the monitor.  As a personal preference, I gear all my 3D to
appear behind the screen, as I have a hard time focusing on stuff leaping out.

	A negative parallax of 2.5 inches on the screen surface will appear
exactly halfway between the surface of the screen and your nose.  A positive
parallax of 2.5 inches on the screen will appear to be at infinity.  You
should avoid positive parallaxes of greater than 2.5", as it will tend to
cause the eyes to diverge.  Eyes are not designed to do this, and if you try
your brain will start taking core dumps.

	Depending on camera seperation, you might be able to get away with
simply shearing the projected image along the projected X axis rather than
actually rotating it (after projection into the viewing frustrum (sp?)).
Computationally, this is a real time-saver.

	Some tips:  By seperating the cameras more and more, but keeping
focused on the same point, you will create a hyperstereo effect, and the
object will appear to be small (since you'll need to cross your eyes to see
it, which you normally do with small objects near your face).  If you get
the left and right images reversed, you'll get a pseudo-stereo effect, which
will also cause your brain to dump core.

	I'd suggest avoiding the red-blue strategy if you can, as the strong
colors tend to give many people headaches.  If you have a short persistence
interlaced display, look into the possibility of using occluding polarized
glasses that flicker in sync with the display.  Full color images are much
prettier to look at, and the flicker is only initially annoying (my eyes
glaze over after a few moments, and I don't notice it anymore).  Select
glasses with a neutral grey filter, and view in a darkened room with minimal
lighting directly in front of you.

	Avoid huge amounts of parallax in either direction.  Trying to touch
the viewer's nose is a bad idea and rarely works.  It's also dependent on
how far the person is from the screen.  A centimeter or three maximum
seperation on the screen at normal viewing distance will produce very
striking and effective results.

	Learn to recognize good and bad 3D.  Closing each of your eyes
independently can help determine what's wrong if your image isn't working
for you.  Holograms are good 3D.  The real world is good 3D (take a good
long look at it sometime).  _Captain Eo_ is bad 3D.

	All this drivel comes from about four solid months of playing around
with 3D on the Amiga under the tutelage of Michael Starks.

	Hope this helps.

_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_
Leo L. Schwab -- The Guy in The Cape	ihnp4!ptsfa -\
 \_ -_		Recumbent Bikes:	      dual ---> !{well,unicom}!ewhac
O----^o	      The Only Way To Fly.	      hplabs / (pronounced "AE-wack")
"Work FOR?  I don't work FOR anybody!  I'm just having fun."  -- The Doctor